Problem: $ B = \left[\begin{array}{rrr}0 & 2 & 2 \\ 2 & 2 & 2 \\ 2 & 2 & 0\end{array}\right]$ What is $ B^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-\frac{1}{2} & \frac{1}{2} & 0 \\ \frac{1}{2} & -\frac{1}{2} & \frac{1}{2} \\ 0 & \frac{1}{2} & -\frac{1}{2}\end{array}\right]$